1. Field of the Invention
The present invention relates to methods for balancing a crankshaft of an engine, and the resultant crankshaft.
2. Description of the Related Art
The typical crankshaft of an internal combustion engine has multiple offset portions which are driven by the piston rods of the engine. To minimize damaging vibration, the crankshaft normally is provided with counterweights which counterbalance the offset portions of the crankshaft.
It is not economically feasible to manufacture the crankshaft and counterweights so that they are totally balanced from the start. Instead, the crankshaft and counterweights normally are manufactured so that they are approximately balanced and then "fine tuned" to bring them into an optimum final static and dynamic balance. This usually is accomplished by selectively removing parts of the counterweights, e.g., by drilling holes in them. U.S. Pat. No. 2,997,882 (Harvey) teaches a machine for such balancing.
It has been known for some time that counterweights or other vibration dampers for engines could at least theoretically be balanced by adding weight to them, much as as slug is added to balance a vehicle wheel. See Harvey and U.S. Pat. No. 3,222,953 (Benjamen). However, as Harvey notes, it is easier to drill out excess material to obtain a precise final balance than to add material. Thus, even where additional material is added, final balancing has still generally been done by drilling. See U.S. Pat. No. 3,748,925 (Stewart). Only recently has it been suggested that it may sometimes be desirable to balance the crankshaft solely by adding weight to the outside of the crankshaft. See U.S. Pat. No. 4,445,399 (Sasaki et al.).
Whenever it has been suggested to add weight, the additional material has been added to the outside of the counterweight or balance member. In modern engines, the clearance tolerances around the crankshaft are quite tight. Thus, there simply is no room to add additional material to the outside of the crankshaft, counterweights or other balancing members.